Device for locally adjusting the tension of an elastic sheet, in particular for a vehicle seat

ABSTRACT

In order to soften or stiffen the support offered by an elastic sheet, and in particular a vehicle seat back, the device comprises a flat spring (1) which is at each of its ends connected to the sheet (38), and fixed to a case (2, 3) containing an inclined disc (10, 12). Two discs are fixed to a control rod (24) which is mounted in the frame (36) of the seat and, when this rod is rotated, they cause the cases to be pivoted symmetrically, so that the spring is extended and stiffens the sheet or is shortened and renders the seat more soft.

Users of motor vehicles no longer hesitate to-day to travel longdistances. Unfortunately, there often results considerable physicalfatigue, and in particular pains due to the compressing of the vertebraebrought about by the prolonged maintenance of the body in the sameposition.

An object of the present invention is to overcome this state of affairsby providing a device for locally adjusting the tension of an elasticsheet more particularly adapted to the adjustment of the seat back of avehicle, which permits a modification of the firmness of the supportprovided locally by the elastic sheet and thus a limitation of thefatigue of the user.

The invention therefore provides a device for adjusting the tension ofan elastic sheet which comprises a flat spring having end portions whichare each fixed to two parallel surfaces between which surfaces a rotarydisc is inserted, the two discs being connected to rotate together butbeing inclined in the opposite direction so that their rotation pivotsin opposite directions the parallel surfaces of the two ends of thespring and results in a modification of the length and the curvature ofthe spring.

Thus, depending on the position of the rotory discs, the flat spring isdisplaced between an extreme position in which it is taut and stiff anda compressed bent extreme position corresponding to maximum flexibility,Between the two positions, the spring is flat at rest and this resultsin its normal elasticity.

The flat spring may easily be associated with an elastic sheet to whichit transmits the tension or the bending imparted thereto by the discs.

Preferably, the spring is a flat sinusoidal spring of the same type asthose making up the elastic sheet.

The rotary discs are mounted on a control rod with which they areconnected to rotate and on which they are inclined.

Such a device is particularly adapted to the adjustment of the supportin a motor vehicle seat. It is then preferably mounted in a lombarsupport region, the control rod being fixed to the uprights of the frameof the seat.

It will of course be understood that the elastic sheet may comprise aplurality of adjustment devices permitting a local modification in itstension in accordance with needs.

A description of an embodiment which is given merely by way of anon-limiting example and shown in the accompanying drawings, will bringout the advantages and features of the invention.

In the drawings:

FIG. 1 is a front elevational view of the end portions of the deviceaccording to the invention, in its position of rest;

FIG. 2 is a top plan view of the device shown in FIG. 1;

FIG. 3 is a diagrammatic view from below of the device in its bentposition;

FIG. 4 is a diagrammatic view of the device shown in FIG. 3 whose springhas been eliminated;

FIG. 5 is a view similar to FIG. 3 of the device in the stiffeningposition;

FIG. 6 is a view similar to FIG. 4 of the position of the discs when thespring is stiffened;

FIGS. 7, 8 and 9 are views of the control discs respectively in thepositions corresponding to FIGS. 1, 3 and 5;

FIG. 10 is a perspective view of a portion of the elastic sheet of theseat back of a vehicle provided with an adjusting device according tothe invention.

As shown in the drawings, the device according to the inventioncomprises a flat spring 1, preferably having a sinusoidal shape, the twoend portions of which each carry a case 2, 3, fixed by a plate 4 to thespring and enclosing between its opposed lateral walls respectively 6and 8 a disc 10, 12. The two discs 10 and 12 are fixed on a rod 14 withrespect to which they are inclined in opposite directions, as clearlyshown in FIG. 1. The two discs 10 and 12 are identical and are thusplaced in a symmetrical manner relative to the median plane of the rod14.

In the position of rest, i.e. the position shown in FIGS. 1 and 2, thediscs 10 and 12 are not in contact with the walls 6, 8 of the cases sothat they exert no force against these walls. In fact, the walls 6 and 8have the shape of a reclining V whose apices 16, 18 are in facingrelation and define consequently a narrow passage whose width isslightly greater than the thickness of the discs 10, 12. The inclinationof the sides 20 of the V's of the walls 6 and 8 substantiallycorresponds to the inclination on the rod 14 of the discs 10, 12 whichare thus simply interposed between the two lateral walls of thecorresponding case.

Each of the walls 6, 8 is provided with an opening 22 which allows thefree passage of the rod 14 and even the rotation of the latter withoutdriving the V's of the walls 6 and 8.

Consequently, when the rod 14, which is preferably provided with acontrol knob 24 which has not been shown in FIGS. 1 to 6, rotates aboutits axis and drives the discs 10 and 12, the latter rub against theapices 16, 18 of the lateral walls 6, 8 and tend to urge back the twowalls of each case in opposite directions. The cases pivot on the rod 14so as to converge either in the direction of the spring 1 or in theopposite direction.

For example, if the rod 14 rotates in the clockwise direction as viewedin FIG. 1, the discs 10 and 12 gradually assume the position shown inFIGS. 3 and 4, i.e. tend to urge the walls 8 toward their end fixed tothe spring 1 while they urge outwardly the end of the walls opposed tothe spring 1. This results in a bending of the spring 1 in the directionof the rod 14 and at the same time a shortening of this spring.

The spring 1 thus bent of course has an increased flexibility.Inversely, if the rod 14 is turned in the counter-clockwise direction,the discs 10 and 12 assume the position shown in FIGS. 5 and 6. In thiscase, each of the discs urges outwardly the wall 6 at its end fixed tothe spring 1 while the two discs bring closer together the ends of thewalls 8 opposed to this spring 1. The spring is consequently taut andextended while assuming a curvature whose concavity faces the rod 14.The extension of the spring stiffens it and reduces its elasticity.

Preferably, each of the cases 2 and 3 includes on the plate 4 for fixingto the spring 1 a projection 26 while the discs 10 and 12 define twoteeth respectively 28 and 30 facing in opposite directions. Thecooperation of the teeth 28 and 30 with the projection 26 limits thedisplacement of the corresponding disc 10 or 12 and consequentlyprovides a signal indicating the arrival of this disc in its extremeposition. Indeed, when the device is in the inactive position shown inFIGS. 1 and 2, each of the discs is in the position shown in FIG. 7. Theprojection 26 of the case is substantially at equal distances from eachof the teeth 28 and 30. Consequently, the rod can turn withoutdifficulty in either direction and rotate the discs fixed thereto.Depending on the direction of rotation of the rod 14, the tooth 28approaches the projection 26 and comes into abutment thereagainst (FIG.8) or the tooth 30 approaches the projection 26 and comes into abutmentthereagainst (FIG. 9).

In each of these two last-mentioned positions, the disc 10, 12 hasslightly passed beyond its unstable position and consequently tends toassume the following stable position constituted by the position offset180° relative to the initial stable position shown in FIG. 7, i.e. tocontinue its rotation. The disc is therefore solidly urged against theprojection 26 and locks itself in the position given thereto. Only arotation of the rod 14 can change the position of the discs 10 and 12and the spring 1.

Such a device permits, owing to the association of the spring 1 with anelastic sheet, a local modification of the tension of this sheet byvarying the curvature and the length of the spring 1.

The elastic sheet may be made in various ways and may be employed in aseat, a box mattress or in any other application. The adjustment ishowever particularly important in the case of vehicle seat backs such asthat partly shown in FIG. 10.

In this case, the rod 14 is mounted in apertures 34 formed in thevertical uprights 36 constituting the frame of the seat and to which theelastic sheet 38 is secured. The device is thus shown behind the elasticsheet, the spring 1 forming a transverse element of this sheet and beingfixed by wire hooks 40 to the longitudinal springs of the sheet 38.

The spring 1 is thus in contact with the various springs. In theposition of rest of the device, the spring 1 has no action on thesprings of the elastic sheet. On the other hand when it is stiffenedunder the action of the discs 10 and 12 and reaches the position shownin FIGS. 5 and 6, it puts the springs 42 of the sheet 38 under tensionand stiffens the seat back in the region in which it is located. On theother hand, when it is shortened and bent in the opposite direction, itimparts an additional elasticity to the whole of the sheet.

Preferably, an adjusting device of the type described hereinbefore willbe mounted in the lumbar support region which is the region the mostsubject to a compressing of the vertebrae when using a vehicle seat.However, it will be understood that this adjusting device may easily bemounted in any other position and that even several adjusting devicesmay be mounted on the same seat back. In this way, the user is in aposition to adjust at any moment the firmness of the support he receivesand adjust it each time he desires.

Likewise, the rod 14 may be rectilinear as shown in FIG. 10, or be bentin its central part, as shown in FIGS. 1 to 6, or even have any othershape enabling it to cause the rotation of the discs 10 and 12 and thedeformation of the spring 1 without affecting the action of the elasticsheet 38 itself.

What is claimed is:
 1. A device for locally adjusting the tension of anelastic sheet, in particular for a vehicle seat back, said devicecomprising a flat spring having two end portions, means defining twoparallel surfaces respectively rigid with each of said end portions, tworotary discs enclosed between said respective parallel surfaces, the twodiscs being connected to rotate with each other but inclined in oppositedirections so that their rotation pivots in opposite directions theparallel surfaces rigid with the two end portions of the spring andbrings about a modification of the length and of the curvature of thespring.
 2. A device according to claim 1, wherein the flat spring has asinusoidal shape.
 3. A device according to claim 2, wherein the rotarydiscs are mounted on a common rod and are inclined in oppositedirections relative to an axis of said rod.
 4. A device according toclaim 1, wherein the distance between the parallel surfaces is suchthat, in a position of rest, the respective disc is free therebetweenand capable of urging them in opposite directions as soon as it is madeto rotate.
 5. A device according to claim 1, wherein the parallelsurfaces are defined by central portions of two lateral walls arrangedas a reclining V having apices which face each other.
 6. A deviceaccording to claim 5, wherein the V-shaped walls are interconnected andform a case for housing the respective disc.
 7. A device according toclaim 5, wherein the sides of the V-shaped walls have inclinations whichcorrespond to the angle of inclination of the discs so that, in theposition of rest, the discs are parallel to the sides of the respectivewalls.
 8. A device according to claim 1, wherein each disc comprises twoteeth and means defining an abutment are provided for cooperation withthe respective disc and stopping the rotation of the disc in a selectedone of two positions corresponding to an extended spring and a shortenedspring.
 9. An elastic sheet, and in particular a vehicle back rest,combined with a frame for the sheet and at least one adjusting devicefor locally adjusting the tension of the elastic sheet, said devicecomprising a flat spring having two end portions, means defining twoparallel surfaces respectively rigid with each of said end portions, tworotary discs enclosed between said respective parallel surfaces, the twodiscs being connected to rotate with each other but inclined in oppositedirections so that their rotation pivots in opposite directions theparallel surfaces rigid with the two end portions of the spring andbrings about a modification of the length and of the curvature of thespring, the lateral frame of the sheet comprising support means for thediscs and the flat spring being connected at end portions thereof toelastically yieldable elements of the sheet and being in contact withall of said elastically yieldable elements so that the extension of thespring locally stiffens them while the shortening of the spring rendersthem more flexible.
 10. A sheet according to claim 9, wherein lateraluprights of the frame are provided with apertures receiving a controlrod of the device controlling the rotation of the discs.
 11. A sheetaccording to claim 9, wherein the device is mounted in a lumbar supportregion of the elastic sheet.